Would France admit it?
I think they would do everything possible to prevent disclosing that if it turns out to be the case.
It would make sense why they would try to hide it, considering that France has the highest population of Muslims in Europe, and it would immediately spark a civil war.
Believe it or not, I visited Paris a few months ago, and the apartment I stayed in was literally 50 feet from the Notre Damn main entrance. One of the first things I noticed was fully armed military and police presence. One of the buildings next to the Notre Damn had been turned into military HQ. Point is they knew that this structure was one of the main targets (along with the Vatican) in Christian Europe in the crosshairs of Islamic terrorists. So I wouldn't be surprised if it turns out to be terrorism and now the French are engaged in a cover up.